This invention relates to a solid wheel turbine having a bucket machined into the perimeter of the wheel. The invention further concerns using a wheel of different diameters such that the discharge flow from the turbine may be guided for an efficiency improvement.
The buckets or blades of turbines are subject to wear or erosion due to a number of factors. In a steam turbine prime mover, for example, the kinetic energy that is absorbed from the steam by the moving blades or buckets and delivered as shaft work to the device being driven results from the expansion of steam into the two-phase region resulting in a lowering in the quality of the steam. As the moisture content rises with the lowering of steam quality, the buckets or blades become more susceptible to erosion. Although wet steam is generally associated with the last stages of a condensing steam turbine, energy recovery from process steam and the advent of geothermal power have resulted in the initial supplying of wet steam, (20-30% quality for geothermal steam and 80% quality for oil well steam injection.) In addition to the presence of water droplets, blade erosion is also a function of the velocity and impingement angle of the moisture particles. The presence of particulates in gases has a similar effect to the presence of water droplets. One solution to blade erosion is the use of replaceable blades.
In U.S. patent application Ser. No. 390,604 filed June 21, 1982 entitled "Solid Wheel Turbine" now abandoned there is disclosed a single or multistage solid wheel turbine having a bucket machined into the perimeter of the wheel. Although this turbine upon testing was found to be suitable for its intended purpose it was ascertained that improvement in efficiency could be obtained by providing additional guidance to the working fluid at the discharge portion of the bucket. The subject matter of this patent application was developed in response thereto and has resulted in a significant improvement in performance. By providing a solid wheel turbine having two sections of different diameters it is possible to divert the high quality steam from the generally half U-shaped bucket into a portion of the wheel defining an L-shaped passageway extending generally radially outward from the U-shaped passageway. In this manner the steam and contaminants being discharged from the bucket are guided outwardly and away from the inlet passage.
This solid wheel turbine retains the advantages of the device disclosed in U.S. patent application Ser. No. 390,604 now abandoned. The present device is capable of very high tip speeds depending upon the type of design and the material used. This turbine is more efficient than a conventional axial flow turbine. This turbine is at least as efficient as a radial inflow turbine, when relatively small power is needed from a relatively high heat drop application, since it has much lower operating rotating speed and therefore incurs smaller, mechanical losses when connected to the device to be driven. The nozzle ring construction is of the radial inflow type with converging or expanding nozzles and low incidence angles for maximizing performance. Because of the bucket geometry and the tangential inflow from the nozzles, moisture droplets or solid particulates moving slower than the gas flow will impinge upon the buckets at low angles and low relative velocity greatly reducing erosion and minimizing braking losses. The inlet and exhaust casings are simply constructed to enable partial-to-full admission of motive fluid at very high pressures. Since the turbine wheel has buckets machined directly into it, bucket failures are essentially impossible. Furthermore, because of the inherent geometrical configuration of the buckets in relation to the disk, induced vibration is virtually eliminated. Integral rotor or thru-bolt construction may be used. With this rugged construction the present invention is suitable for a wide range of gases, either superheated or saturated. By using an appropriate gear reduction unit any output shaft speed is obtainable at optimum turbine efficiency.
Since the herein described turbine wheel has two portions of varying diameters, it is possible to either manufacture the wheel as a single element and thereafter machine the passages into the wheel or the wheel may be manufactured as two cylindrical portions each being machined with the appropriate structure and then the two being combined to form the turbine wheel.